DESCRIPTION (Taken from the application): Fibrosis, the excessive deposition of extracellular matrix, is a major complication of many inflammatory disorders, including rheumatic diseases, which are characterized by T cell infiltration. Our goal is to characterize novel mechanisms by which activated T cells regulate fibroblast proliferation and collagen production. This proposal will focus on interactions between soluble factors (IL-4 and IFN-7) and T cell-fibroblast contacts (CD40-CD40L interactions) in the regulation of collagen production. Our overall hypothesis is that cell surface interactions between activated T cells and fibroblasts regulate the balance of pro-fibrotic and anti-fibrotic influences of cytokines. The specific hypothesis of this study is that IL-4 and IFN-y effects on fibroblast proliferation and collagen production are modulated by CD40-CD40L interaction, which shifts the overall balance toward IL-4 effects. Thus, we propose that CD40 ligation can be synergistic with IL-4 signals in fibroblasts, analogous to the well-known synergy between CD40 ligation and IL-4 m the regulation of immunoglobulin production by B cells. By synergy we designate a combined action of two factors that has higher amplitude than a sum of two effects of the factors alone. We also propose that CD40 ligation can be antagonistic to the antfibrotic effects of IFNy. This proposal will test how CD40 ligation functionally affects the pro-/anti-fibrotic balance between IL-4 and IFN-7. It will also examine potential mechanisms of interaction between CD40 ligation and IL-4, particularly through activation of intracellular signaling molecules. This proposal will address the following specific objectives: 1. Define the effects of CD40 ligation on the pro-fibrotic actions of IL-4 and anti-fibrotic actions of IFN-y on fibroblast proliferation and collagen production. The effects ofCD40 ligation and IL-4 will be defined when two cytokines are tested alone, in combination, or in the context oft cell-fibroblast co-cultures. 2. Determine mechanisms of synergy between CD40 ligation and IL-4 on fibroblast proliferation. Experiments will focus on protein.tyrosine kinase (PTK) signal transduction pathways, but will also test contribution of modulation of receptor expression. The significance of this research is that it focuses on novel mechanisms of regulating fibrosis by. immune cells. The proposed study may contribute to our understanding of the role T cells in the development of fibrosis and lead to novel therapeutic approaches in these diseases.